Stigma perpetuated by health-care providers has been found to be a barrier to care for vulnerable populations, including HIV-infected, people who inject drugs (PWIDs), and men who have sex with men (MSM) in multiple clinical contexts and remains unexamined among professional health-care students in Malaysia. This cross-sectional, anonymous, and Internet-based survey assessed the attitudes of medical and dental students toward HIV-infected, PWID, and MSM patients. Survey invitation was emailed to 3191 students at 8 professional schools; 1296 (40.6%) responded and scored their attitudes toward these patient groups using a feeling thermometer, indicating their attitudes on a sliding scale from 0 (most negative) to 100 (most positive). Compared to general patients (mean = 76.50), the mean scores for HIV-infected (mean = 54.04; p < 0.001), PWID (mean = 37.50; p < 0.001), and MSM (mean = 32.13; p < 0.001) patients were significantly lower and significantly different between each group comparison. Within group differences, most notably religion, ethnicity, and personally knowing someone from these populations were associated with significant differences in attitudes. No differences were noted between pre-clinical and clinical year of training. Health-care students represent the next generation of clinicians who will be responsible for future HIV prevention and treatment efforts. Our findings suggest alarmingly negative attitudes toward these patients, especially MSM, necessitating prompt and effective interventions designed to ameliorate the negative attitudes of health-care students toward vulnerable populations, specifically HIV-infected, PWID, and MSM patients in Malaysia.